Integrated circuits (ICs) may include transceiver circuitry that includes high-speed receivers and transmitters that may be used in various types of applications. Generally, an inductance-capacitance voltage-controlled oscillator (LC-VCO) circuit is used to control the tuning frequency of the transceiver circuitry on an IC. Accordingly, the tuning range of the transceiver circuitry is determined by the tuning range of the LC-VCO circuit that controls the transceiver circuitry.
As is generally known, an LC-VCO circuit may include an inductor (L) (or inductors) and variable capacitors or varactors (C). Even though an LC-VCO circuit with a wide frequency tuning range is generally desired, the tuning range of an LC-VCO circuit is typically limited by the minimum and maximum capacitance values of the varactors in the LC-VCO circuit. A capacitor array with metal-oxide-semiconductor field-effect transistor (MOSFET) switches is usually used to enlarge the tuning range of an LC-VCO circuit. However, the capacitor array with MOSFET switches typically occupies additional die area and hence increases the overall die area required for the LC-VCO circuit.
For high-speed circuitry, inductors with a high quality factor (Q) are preferred. Achieving high Q is generally challenging due to inductor loss that results from current flowing from the inductor to the substrate of the IC. To improve Q, a patterned ground shield is conventionally used to isolate the inductor from the substrate. However, the patterned ground shield may introduce a fixed parasitic capacitance to the LC-VCO circuit. Parasitic capacitance is undesirable because it reduces the tuning range and limits the resonance frequency of the LC-VCO circuit.
It is within this context that the embodiments described herein arise.